It is a common problem in vehicles such as large trucks that during travel there is created a low pressure void behind the vehicle during travel and such low pressure void creates considerable drag on the speed of the vehicle which adds considerably to the cost of fuel consumption.
U.S. Pat. No. 4,320,920 provides an air deflector for reducing turbulence and drag at the rear area of vehicles having an elongate cellular structure having inner and outer plates spaced apart by a plurality of deflector ribs. The deflector can be shaped to the contour of a specific vehicle configuration such as being located on the roof of a vehicle adjacent a respective rear door. This air deflector was complicated in structure and was deficient in that it only diverted air perpendicularly into the rear plane of the vehicle to which it was attached and thus did not achieve an efficient and widespread dissemination of air or wind currents travelling along the roof of the vehicle.
U.S. Pat. No. 5,171,057 provided an air diversion apparatus which comprised of a plurality of L shaped air duct members each having a horizontal air intake component and a vertical component having an air outlet wherein the horizontal component was located on the vehicle roof and the vertical component was attached to a rear door of the vehicle. However such air diversion apparatus was complicated in structure in that the air intake opening of the horizontal component was in fluid communication with fluid conduits connected to a fluid reservoir having a fluid reservoir for cleaning operations. Also the air outlet was the only way wind currents could be disseminated from the vehicle which reduced drag reduction efficiency. Also opening or closing of the vehicle doors would have been relatively difficult because the horizontal component was described as being mounted to the roof of the vehicle or fixedly mounted to the vehicle roof.
Reference also may be made to U.S. Pat. No. 6,779,834 which described drag reduction apparatus having a tapered section attached to a roof, an elbow interconnecting the tapered section, and a duct section attached to a rear door of the vehicle. Opening or closing of the rear doors would have been difficult because the elbow engaged with an adjacent open end of the tapered section and also such engagement would have created leakage of air or wind currents which would have detracted from the drag reduction efficiency of the drag reduction apparatus. However the major problem of this prior art was that it was necessary to attach the tapered section to the roof by fasteners and thus installation would have been time consuming and labour intensive. Also the only air outlets provided were in the centre of the duct section as well as at a bottom end of the duct section and this also would have adversely affected operational efficiency.